The present invention relates generally to a method of correcting unbalance of a rotor of an electric motor or the like and more particularly to a method wherein dynamic unbalance of a rotor is corrected by either adding or subtracting corrective weights by machining the rotor in an axial direction thereof.
A conventional method of determining or modifying a corrective weight of a measured unbalanced weight of a rotor involves making a hole or holes in a radial direction of the rotor. Since the depth of a drill cutting such a hole is not proportional to the corrected mass achieved thereby, the corrective mass must be corrected or modified.
Some rotors have a structure which is not easily drilled in the radial direction because the rotors have a laminated core. In such a case, it is necessary to correct unbalance by machining the rotor with a milling cutter or drill fed in a direction parallel to the rotor axis. In such a case, however, residual unbalance is still apt to occur because there is a deviation in the center of gravity resulting from removal of weight from a correcting plane. The occurrence of the residual unbalance is known as a correcting plane. The correcting plane is generally located in the vicinity of one end of the rotor. The correcting plane error of course affects the corrected mass of the plane in proximity to said one end of the rotor. In addition, the correcting plane error affects another correcting plane, located in the vicinity of the other end of the rotor. Thereby, recorrection of the corrective masses in both of the correcting planes has been thought to be impossible.
In the prior art techniques, the correcting plane errors are avoided by making the corrective machining length in the direction of the rotor axis as small as possible. In the prior art milling machine method the removing weight center of gravity is always at the same position. If the distance between two correcting planes is very small, the ratio between the unbalanced weight, after correction, and the initial unbalanced weight is only 1/2 to 1/4. Therefore, to obtain the necessary dynamic balance it has been previously necessary to repeat the measurements and corrections several times, for either automatic or manual correction. Thereby, the prior art method for balancing a rotor requires a long time; the costs to perform the balancing operation and the equipment therefor are high.